Most fleas collected from rats trapped in downtown Los
Angeles, California carried microbes from the genus, Bartonella, many of which are human pathogens, according to a paper
in the November Applied and Environmental
Microbiology.

The research team limited their investigation to fleas of
the species Xenopsylla cheopis,
because they are known both to infest Rattus
norvegicus, the Norway rat, which is a major pest in high density urban
areas, as well as to bite humans, says first author Sarah Billeter of the
Centers for Disease Control and Prevention, Fort Collins, CO.

Bartonella species
are gram-negative bacteria that infect red blood cells and endothelial cells of
the host. More than half are thought to cause some clinical disease in humans. B. rochalimae, found in 72 percent of
the collected fleas, was first isolated from the blood of a patient who became
ill after returning to the United States from a vacation in Peru, says
Billeter. “She complained of fever, insomnia, nausea, headache, and mild cough.
Upon examination at the hospital, she was found to have recurrent fever,
splenomegaly, and anemia.” B. rochalimae
has also been identified as a cause of infectious endocarditis in a dog from
San Francisco, says Billeter.

The remaining fleas harbored sequences most closely related
to B. tribocorum, a bacterium that
has been detected in rodents “from various parts of the world,” including
France, says Billeter, and was isolated from the blood of a febrile Thai
patient. “At this point, it remains unclear whether B. tribocorum is a human pathogen,” says Billeter. “From a public
health standpoint, however, it is important to determine whether R. norvegicus are reservoirs for
zoonotic Bartonella spp. due to their
close contact with humans and their pets.” The question of whether X. cheopis can actually spread such
pathogens to humans also warrants further investigation, says Billeter.